1. Field of the Invention
The present invention pertains to a process for drying a paper web, particularly for the production of toilet paper.
As is well known in the production of paper, initially a wet web is formed which subsequently must be drained and dried in order to render the paper usable. Therefore, processes can be used which require a relatively large steam heated drying cylinder. Such cylinders, whose production and assembly are quite expensive, are also known as Yankee-cylinders. They approach a diameter of over 5 meters and are activated with steam pressure in the cylinder up to 8 bar.
2. Discussion of the Background of the Invention and Material Information
With known creping processes, by means of a scraper, the dried paper web, adhered on a surface, can be buckled or upset on the hot press roll at its removal therefrom. Other possibilities are also known, for example for finish drying a web, with a dry weight of below 95%, on a separate creping cylinder and thereafter creping same.
Additional processes for formal drainage are known to those skilled in the art, for example, as taught in German patent publication DE 3705241. This process pertains to a very special technology, in which steam is produced in a press gap or compression gap, with the steam driving the water from the paper web which is then taken or absorbed by the felts running through the press and are removed therefrom as water, steam or condensate. In this manner, a portion of the moisture is effectively and quickly removed. Often such processes are utilized in the process having elongated gaps, that are known as shoe presses or wide-nip presses. After running through the hot press gap, the paper web becomes free and can filter out steam. It is, however, suddenly exposed to the very much lower ambient pressure, whereby the steam pressure of the overheated remaining water, depending on each type and area weight of the web, can lead to different destructions or injuries, for example, delaminations of the paper web via "flash steam". The possibilities of the process are therefore limited to specific types of paper. Through suitable measures, often requiring considerable technical control expenditures, safe operation can be achieved, during which the steam pressure, at the press gap, is limited to a value below ambient pressure at the cost of reduced drainage effect.